Heater built-in valve

Abstract

A heater built-in valve usable even under a high-temperature condition beyond 200° C. is provided. Piston driving means 7 has an upper compressed-air introducing chamber 24 for moving a piston 6 downward, and a lower compressed-air introducing chamber 25 for moving the piston 6 upward. Piston sealing means 8 has an upper bellows 29 that seals the upper compressed-air introducing chamber 24 , and a lower bellows 30 that seals the lower compressed air introducing chamber 25.

The invention claimed is: 
     
       1. A heater built-in valve comprising
 a valve box provided with a fluid passage, a casing provided above the valve box, 
 a valve rod that moves up and down a valve element opening and closing the fluid passage, 
 a piston that is arranged movably upward and downward inside the casing and is fixed to the valve rod, 
 piston driving means for moving up and down the piston, 
 heating means for heating a vicinity of the valve element, and 
 sealing means for sealing between the piston and the casing, 
 the heater built-in valve, wherein 
 the piston driving means has an upper compressed-air introducing chamber for moving the piston downward, and a lower compressed-air introducing chamber for moving the piston upward, and 
 the sealing means has an upper bellows that seals the upper compressed-air introducing chamber, and a lower bellows that seals the lower compressed-air introducing chamber, 
 the piston includes a large-diameter cylindrical part and a small-diameter cylindrical part that continues below the large-diameter cylindrical part, and 
 a first upper bellows which upper end is placed above an upper end of the piston large-diameter cylindrical part, and which is arranged inside the piston large-diameter cylindrical part, and 
 a second upper bellows which upper end is placed above the upper end of the piston large-diameter cylindrical part, and which is arranged outside the piston large-diameter cylindrical part, respectively, so that 
 bellows receiving parts that support the upper end portions of the respective bellows are provided in an upper portion of the casing, by which 
 the upper compressed-air introducing chamber is formed by an upper end surface of the piston large-diameter cylindrical part, the upper portion of the casing, the first upper bellows and the second upper bellows, while 
 a lower bellows is arranged outside the piston small-diameter cylindrical part, and 
 a bellows receiving part that supports a lower end surface of the lower bellows is provided in a circumferential wall of the casing, by which 
 the lower compressed-air introducing chamber is formed by the circumferential wall of the casing, the second upper bellows, a lower end portion of the piston large-diameter cylindrical part and the lower bellows. 
 
     
     
       2. The heater built-in valve according to  claim 1 , wherein
 the valve rod is made hollow, and 
 a heater and a sensor of the heating means are arranged inside of the valve rod, and 
 a lead wire of the heating means is pulled out from an opening at an upper end of the valve rod to be drawn out from a top wall of the casing. 
 
     
     
       3. The heater built-in valve according to  claim 1 , wherein
 a through-hole into which a lead wire of the heating means is inserted and which is provided in the casing, and 
 a joint for drawing the lead wire of the heating means to outside is attached to a circumferential edge portion of this through-hole, 
 the joint having the same configuration as joints for connecting piping to the upper compressed-air introducing chamber and the lower compressed-air introducing chamber. 
 
     
     
       4. The heater built-in valve according to  claim 3 , wherein
 the joint for drawing the lead wire of the heating means to outside has
 a first sleeve fixed to the circumferential edge portion of the through-hole, 
 a cap nut rotatably fitted onto the first sleeve, 
 a second sleeve connected to the first sleeve with a gasket interposed, and 
 a male screw member that is fitted onto the second sleeve and is screwed into the cap nut. 
 
 
     
     
       5. The heater built-in valve according to  claim 1 , wherein special coating is applied to a sliding portion. 
     
     
       6. The heater built-in valve according to  claim 5 , wherein the special coating is coating with nonelectrolytic plating treatment. 
     
     
       7. The heater built-in valve according to  claim 6 , wherein
 a nonelectrolytic plating layer is made of any one of nickel-phosphorous based, cobalt-phosphorous based, nickel-phosphorous-tungsten based, nickel-boron based, and nickel-boron-tungsten based nonelectrolytic plating layers. 
 
     
     
       8. The heater built-in valve according to  claim 1 , wherein
 the heating means has a heater that is attached to the valve rod so as to be movable together with the valve rod, and 
 a lower end surface of the heater abuts against the valve element. 
 
     
     
       9. The heater built-in valve according to  claim 1 , wherein
 the heating means has a heater that is attached to a heater holding member fixed to the casing so as not to move with the movement of the valve rod, and 
 a lower end surface of the heater abuts against the valve element in an opening position where the valve rod has moved upward.